Pellicle for flat panel display photomask

ABSTRACT

A pellicle assembly for large-size photomasks including a frame member configured to be affixed to a large-size photomask substrate, a substantially rigid and transparent pellicle membrane affixed to the frame member so as to protect at least a portion of the large-size photomask substrate from contamination during usage, storage and/or transport, and a coating on at least one of top and bottom surfaces of the pellicle membrane that binds the pellicle membrane to prevent separation of pellicle membrane material in the event of breakage.

RELATED APPLICATIONS

This application is a continuation application that claims priority toand the benefit of U.S. application Ser. No. 16/568,365, filed Sep. 12,2019, and entitled PELLICLE FOR FLAT PANEL DISPLAY PHOTOMASK, whichclaims priority to and the benefit of Provisional Application No.62/730,119, filed Sep. 12, 2018 and entitled PELLICLE FOR FLAT PANELDISPLAY PHOTOMASK, the contents of all of which are incorporated hereinby reference in their entirety.

FIELD OF THE INVENTION

The present invention generally relates to photomask pellicles, and inparticular to pellicles intended for use with large-size photomasks.

BACKGROUND

Flat-panel displays (FPDs) are electronic viewing technologies used todisplay content (e.g., still images, moving images, text, or othervisual material) in a range of entertainment, consumer electronic,personal computer, and mobile devices, and many types of medical,transportation and industrial equipment. The current FPD types include,for example, LCD (Liquid Chrystal Display), AM LCD (Active Matrix LiquidChrystal Display), OLED (Organic Light Emission Diode), LED (LightEmitting Diode), PDP (Plasma Display Panel) and AMOLED (Active MatrixOLED).

During manufacture of an FPD, an FPD lithography system irradiates lightonto a photomask on which the original thin-film-transistor (TFT)circuit patterns are drawn, and the light exposes the patterns onto aglass plate substrate through a lens. On a large glass plate, theexposure process is repeated several times in order to form the patternsonto the entire plate.

Driven by end-user demands for better product quality and lower costs,FPD manufacturers are constantly searching for improved processequipment. Larger and thinner glass plates as well as tighterrequirements lead to new challenges for equipment manufacturers. Theglass plates are categorized by size and named by generations (GEN). Forinstance, Gen 8.5 glass plates have a size of 2200×2500 mm and canproduce the panels needed for 55-inch LCD televisions. Photomasks mustfollow the size of FPD generations, because they are used as originalplates to transfer patterns to TFT and color filter substrates.

As the size of photomasks used to manufacture large-size FPDs increases,a number of challenges arise in avoiding contamination of suchphotomasks by dust or other particles that might cause unwantedartifacts on the glass plate during the FPD lithography process. In thisregard, conventional, smaller-sized photomasks may include a pellicle,which is a thin, transparent membrane or film that protects thephotomask surface from contamination. However, the use of such pellicleswith large-size photomasks requires an enhanced pellicle design thatwill function effectively over a large area.

SUMMARY OF THE INVENTION

A pellicle assembly for large-size photomasks according to an exemplaryembodiment of the present invention comprises: a frame member configuredto be affixed to a large-size photomask substrate; a substantially rigidand transparent pellicle membrane affixed to the frame member so as toprotect at least a portion of the large-size photomask substrate fromcontamination during usage, storage and/or transport; and a coating onat least one of top and bottom surfaces of the pellicle membrane thatbinds the at least one of the top and bottom surfaces of the pelliclemembrane to prevent separation of pellicle membrane material in theevent of breakage.

In exemplary embodiments, the pellicle membrane is spaced from thephotomask substrate by a distance of 3 mm to 20 mm.

In exemplary embodiments, the pellicle membrane is affixed to the framemember by adhesive.

In exemplary embodiments, the pellicle membrane is affixed to the framemember by a clamping mechanism.

In exemplary embodiments, the pellicle membrane has a transparency of atleast 90% over a wavelength range of 190 nm to 500 nm.

In exemplary embodiments, the pellicle membrane has the followingdimensions: outer dimension of 1146.0 mm×1366.0 mm and inner dimensionof 1122.0 mm×1342.0 mm.

In exemplary embodiments, the pellicle membrane has the followingdimensions: outer dimension of 1526.0 mm×1748.0 mm and inner dimensionof 1493.0 mm×1711.0 mm.

In exemplary embodiments, the pellicle membrane has a thickness of 4 μm.

In exemplary embodiments, the pellicle membrane is made up of fusedsilica.

In exemplary embodiments, the coating meets wavelength requirements from190 nm to 500 nm.

In exemplary embodiments, the pellicle assembly and photomask substrateare subjected to a compensation procedure within an exposure tool systemto correct for any distortions induced by the pellicle.

In exemplary embodiments, the large-size photomask substrate isconfigured to manufacture a flat panel display.

In exemplary embodiments, the flat panel display is LCD (Liquid ChrystalDisplay), AM LCD (Active Matrix Liquid Chrystal Display), OLED (OrganicLight Emission Diode), LED (Light Emitting Diode), PDP (Plasma DisplayPanel) or AMOLED (Active Matrix OLED).

These and other features and advantages of the present invention will bepresented in more detail in the following detailed description and theaccompanying figures which illustrate by way of example principles ofthe invention.

DESCRIPTION OF THE DRAWINGS

Various exemplary embodiments of this invention will be described indetail, with reference to the following figures, wherein:

FIG. 1 is a cross-sectional view of a large-size photomask assemblyaccording to an exemplary embodiment of the present invention;

FIG. 2 is a top plan view of a large-size photomask assembly accordingto an exemplary embodiment of the present invention;

FIG. 3 is a partial cross-sectional view of a large-size photomaskassembly according to an exemplary embodiment of the present invention;and

FIG. 4 is a flowchart of a process for compensating for mask or pellicleweight induced distortions according to an exemplary embodiment of thepresent invention.

DETAILED DESCRIPTION

FIG. 1 depicts a large-size photomask assembly, generally designated byreference number 1, configured in accordance with an exemplaryembodiment of the present invention. The photomask assembly 1 includes alarge-size photomask (or reticle) 20 comprised of a substantiallytransparent substrate 22 to which one or more patterned layers ofmasking material 24 are affixed. The patterned layer of masking material24 represents a scaled image of the pattern desired to be created on aglass panel of an FPD. The substrate may be comprised of fused silicaand the masking material may be comprised of chromium. In exemplaryembodiments, other types of materials may be used to form the photomaskso that the present invention is not limited for use with photomaskshaving fused silica substrates and chromium masking material. Further,in exemplary embodiments, the pellicle of the instant invention can beused in conjunction with all types of photomasks including, but notlimited to, binary masks and phase shift masks (PSM).

The large-size photomask 20 may be appropriately sized to accommodatephotolithography processing of glass plate substrates used to form FPDs.In accordance with an exemplary embodiment, the large-size photomask 20has dimensions of 1220 mm×1400 mm for Generation 8.5 size glass plates(e.g., glass plates having dimensions of 2200 mm×2500 mm). In anotherexemplary embodiment, the photomask 20 has dimensions of 3400 mm×3000 mmfor Generation 10.5 size glass plates (e.g., glass plates havingdimensions of 3370 mm×2940 mm). In exemplary embodiments, the large-sizephotomask 20 may be appropriately sized for photolithographic processingup to Generation 10.5 glass plate substrates and beyond as technologyadvances. For example, the large size photomask 20 may have dimensionsin the range of 390 mm×610 mm (Generation 3) to 3400 mm×3000 mm(Generation 10.5).

As further shown in FIG. 2, photomask 20 also includes a pellicle frameor ring 26 which extends around the perimeter of the patterned maskingmaterial 24. In an exemplary embodiment, frame 26 is made of anodizedaluminum alloy, however, other materials may be used as well. Althoughshown as a continuous ring, in exemplary embodiments the frame 26 mayhave other shapes and may include various gaps or vents to ensure thatpressure within the gap between pellicle and photomask comes toequilibrium at the end user site. Frame 26 is affixed to substrate 22using adhesive 27, such as, for example, hot-melt adhesive (HMA). In anexemplary embodiment, the HMA is styrene polymer. A liner 25 may bedisposed between the adhesive 27 and the surface of the photomasksubstrate 22. In an exemplary embodiment, the liner 25 is a polyesterfilm.

In exemplary embodiments, the frame 26 may include one or more vents 21configured to allow for equalization of pressure between the interiorspace formed below the pellicle membrane 28 and atmosphere. Each vent 23may include a filter 23 that allows air and/or other gasses to passthrough while filtering out particles.

The photomask assembly 1 further includes a pellicle membrane 28disposed over the photomask 20. In this regard, the pellicle membrane 28may be affixed to the frame 26 by an adhesive 29, such as, for example,a UV-curable adhesive. In an exemplary embodiment, the adhesive 29 usedto affix the pellicle membrane 28 to the frame 26 has sufficientmechanical strength so as to withstand 30 psi air blow at a 1 inchdistance. The pellicle membrane 28 generally conforms to the dimensionsof the frame 26. One or more of the edges or corners of the pelliclemembrane 28 may be beveled or rounded for safety reasons.

The pellicle membrane 28 may be coated with one or more anti-reflectivematerials to give it suitable anti-reflective properties. Theanti-reflective coating process can be done by spin-coating or vacuumdeposition with low refractive index materials, examples of whichinclude fluoropolymers, thin layers of oxides and oxynitrides such asTaO and TaON. In exemplary embodiments, the pellicle membrane 28 mayinclude a coating that binds the surface to prevent the pelliclematerial from separating in the event of breakage. This coatingpreferably meets wavelength requirements from 190 nm to 500 nm.

In exemplary embodiments, the pellicle membrane 28 is made of celluloseester or perfluoropolymer. In other exemplary embodiments, the pelliclemembrane 28 may be a flat, polished, low birefringence slice of fusedsilica, as described in U.S. Pat. No. 6,524,754, the entire contents ofwhich are incorporated herein by reference. The fused silica materialused to form the pellicle membrane 28 may have the properties listed inTable 1. The transfer of the photomask image to the semiconductor waferoccurs through a process commonly referred to as photolithography. Morespecifically, a wafer exposure system is used to interpose the photomaskbetween a semiconductor wafer which is coated with a layer ofphotosensitive material and an optical energy source. Energy from thewafer exposure system is inhibited from passing through the areas of thephotomask in which the masking material is present. However, energygenerated by the water exposure system passes through the portions ofthe substrate of the photomask not covered by the masking material andcauses a reaction in the photosensitive material on the semiconductorwafer. Through subsequent processing, the image created on thephotosensitive material is transferred to the semiconductor wafer.

TABLE 1 Units of Measure SUMetrIc (Imperial) Mechanical Density gm/cc(Ib/fe³)   2.2   (137.4) Porosity % (%)   0     0 Color — clear —Flexural Strength MPa (Ib/in² × 10³) — — Elastic Modulus GPa (Ib/in² ×10⁶)   73     (10.6) Shear Modulus GPa (Ib/in² × 10⁶)   31     (4.5)Bulk Modulus GPa (Ib/in² × 10⁶)   41     (6) Poisson's Ratio —   0.17  (0.17) Compressive Strength MPa (Ib/in² × 10³)   1108      (160.7)Hardness Kg/mm²   600      — Fracture Toughness K_(IC) MPa · m^(1/2) — —Maximum Use Temperature ° C. (° F.)   1100      (2000) (no load) ThermalThermal Conductivity W/m · ° K   1.38   (9.6) (BTU · in/ft² · hr · ° F.)Coefficient of Thermal 10⁻⁶/C. (10⁻⁶/° F.)   0.55   (.31) ExpansionSpecific Heat J/Kg · ° (Btu/lb · ° F.)   740      (0.18) ElectricalDielectric Strength ac-kv/mm   30     (750) ((volts/mil) DielectricConstant @ 1 MHz   3.82   (3.82) Dissipation Factor @ 1 MHz   0.00002(0.00002) Loss Tangent @ 1 MHz — — Volume Resistivity ohm · cm >10¹⁰    —

In exemplary embodiments, the pellicle membrane 28 preferably has atransmittance of ≥90% over a wavelength range of 190 nm to 500 nm with astand off distance of 3 mm to 20 mm, and filters out particles that are≥10 μm in size.

In an exemplary embodiment, in order to accommodate Generation 8.5 glassplate substrates, the pellicle membrane 28 may have one or more of thefollowing characteristics: outer dimension of 1146.0 mm×1366.0 mm (+0.0,−4.0); inner dimension of 1122.0 mm×1342.0 mm (+0.0, −4.0); pelliclethickness of 4 μm (±0.2 μm); pellicle transmittance of ≥95% (averagebetween 360 nm and 440 nm); pellicle frame material is aluminum alloy(black anodized); stand off of 7.0 mm (±0.2 mm). For the purposes of thepresent disclosure, the term “inner dimension” of the pellicle membranemay be defined as an orthogonal measurement of the inner most parts ofthe frame and the “outer dimension” of the pellicle membrane may bedefined as an orthogonal measurement of the outer most parts of theframe.

In an exemplary embodiment, in order to accommodate Generation 10.5glass plate substrates, the pellicle membrane 28 may have one or more ofthe following characteristics: outer dimension of 1526.0 mm×1748.0 mm(+0.0, −4.0); inner dimension of 1493.0 mm×1711.0 mm (+0.0, −4.0);pellicle thickness of 4 μm; pellicle transmittance of ≥95% (averagebetween 360 and 440 nm); pellicle frame material is aluminum alloy(black anodized); stand off of 8.0 mm (±0.2 mm).

In exemplary embodiments, the pellicle membrane 28 may be secured to theframe using a removable frame assembly so that the pellicle can beeasily removed and cleaned. For example, as shown in the cross-sectionalview of FIG. 2, frame 42 made from anodized aluminum is affixed tosubstrate 22 by means of an adhesive, applicable types of which beingwell known in the art. Those skilled in the art will understand frame 42can be made from materials other than anodized aluminum. In thepreferred embodiment frame 42 extends around the entire perimeter of thepatterned masking material, however, frame 42 need not be contiguous andmay include one or more gaps. Frame 42 includes a first receptive area44 which forms a shelf parallel to the surface of substrate 22 forreceiving the lower surface of the outer edges of pellicle 28. Frame 42also includes a second receptive area or detent 46 which receives lowerprotrusion 52 of flexible retainer 50 which may be constructed from avariety of materials including plastics and polytetrafluoroethylene(e.g., Teflon). An upper protrusion 54 of retainer 50 extends over thefirst receptive area 44 of frame 42 and over the upper surface of theouter edge of pellicle 28 thereby holding pellicle 28 securely in place.Accordingly, in this embodiment there may be no need for adhesive toaffix the pellicle to the frame. For aid in the installation and removalof flexible retainer 50, the corners of retainer 50 may include flexibletabs 56. When an upward force is exerted on flexible tabs 56, lowerprotrusion 52 is decoupled from second receptive area 46 of frame 42.With lower protrusion 52 decoupled from frame 42, retainer 50 can beremoved thereby enabling pellicle 28 to be removed as well.

In this embodiment, no vent is necessary in frame 42 since pressure canbe relieved through the gaps between frame 42, pellicle 28, and retainer50. Additionally, since no adhesive is used to secure the pellicle tothe frame, the pellicle can be more readily removed, cleaned, and/orreplaced.

In exemplary embodiments, compensation within or on the pelliclemembrane material itself may be used to correct for mask or pellicleweight induced distortions. In this regard, finished blanks may bepaired with flat panel design layers to optimize flat panel maskmanufacturing. Large area mask blank manufacturing data may be usedalong with required display lithography pattern design data and anunderstanding of the mask and lithographic process to pair and tunefinished blanks to design for mask making optimization and yieldimprovement. As shown in FIG. 4, in exemplary embodiments, this processmay involve one or more of the following steps:

Step S1: Actual mask blank manufacturing data including but not limitedto blank flatness, defects (size and placement), film properties areoverlaid with the proposed mask design pattern;

Step S2: Pairing and optimization is performed. This pairing andoptimization may include shifting and adjustment of flat panellithography design data to best match with the measured blankcharacteristics with aim to improve finished mask yield and performancein the intended application. The pairing and optimization may beperformed by simulating the overlay of manufactured blank or blanksproperties with the intended design data.

Step S3: An optimum blank is selected from a batch based on thesimulation for the specific use and/or the pattern data may be scaled,tuned, embellished, rotated or otherwise manipulated to be compatiblewith the proposed blank to be used in the flat panel mask makingoperation.

Once the blank and mask design pattern elements are optimally mergedthen the mask is committed to manufacturing using the selected blank andthe optimization parameters. The subsequent mask manufacturing processmay access and track the overlaid mask-blank conditions, and theinspection and other mask making steps for flat panel display masks mayuse these conditions to tune or optimize the manufacturing flow.

While in the foregoing specification a detailed description of aspecific embodiment of the invention was set forth, it will beunderstood that many of the details herein given may be variedconsiderably by those skilled in the art without departing from thespirit and scope of the invention.

1. A method of manufacturing a flat-panel display, comprising: disposinga large-size photomask between an optical energy source and a glassplate substrate, the large-size photomask comprising: a large-sizephotomask substrate; at least one circuit pattern formed on thelarge-size photomask substrate; a frame member; a substantially rigidand transparent pellicle membrane affixed to the frame member so as toprotect at least a portion of the large-size photomask substrate fromcontamination during usage, storage and/or transport; and a coating onat least one of top and bottom surfaces of the pellicle membrane thatbinds the at least one of the top and bottom surfaces of the pelliclemembrane to prevent separation of pellicle membrane material in theevent of breakage; irradiating light from the optical energy sourcethrough the large-size photomask and onto the glass plate substrate in aphotolithographic process so that the at least one circuit pattern istransferred from the large-size photomask to the glass plate substrate.2. The method of claim 1, wherein the pellicle membrane is spaced fromthe photomask substrate by a distance of 3 mm to 20 mm.
 3. The method ofclaim 1, wherein the pellicle membrane is affixed to the frame member byadhesive.
 4. The method of claim 1, wherein the pellicle membrane isaffixed to the frame member by a clamping mechanism.
 5. The method ofclaim 1, wherein the pellicle membrane has a transparency of at least90% over a wavelength range of 190 nm to 500 nm.
 6. The method of claim1, wherein the pellicle membrane has the following dimensions: outerdimension of approximately 1146.0 mm×1366.0 mm and inner dimension ofapproximately 1122.0 mm×1342.0 mm.
 7. The method of claim 1, wherein thepellicle membrane has the following dimensions: outer dimension ofapproximately 1526.0 mm×1748.0 mm and inner dimension of approximately1493.0 mm×1711.0 mm.
 8. The method of claim 1, wherein the pelliclemembrane has a thickness of approximately 4 μm.
 9. The method of claim1, wherein the pellicle membrane is made up of fused silica.
 10. Themethod of claim 1, wherein the coating meets wavelength requirementsfrom approximately 190 nm to approximately 500 nm.
 11. The method ofclaim 1, further comprising: obtaining large area mask blankmanufacturing data corresponding to one or more large area mask blanks;simulating performance of the large area mask blanks by overlayingpattern data associated with the at least one circuit pattern on themask blank manufacturing data; optimizing the photolithographic processbased on the simulated performance by pairing one of the one or morelarge area mask blanks with the pattern data; and manufacturing thelarge area photomask from the one of the one or more large area maskblanks.
 12. The method of claim 11, further comprising manipulating thepattern data paired with the one of the one or more large area maskblanks.
 13. The method of claim 1, wherein the flat-panel display is aliquid crystal display, an active matrix liquid crystal display, anorganic light emission diode, a light emitting diode, a plasma displaypanel, or an active matrix organic light emission diode.
 14. The methodof claim 1, wherein the large-size photomask is configured to form alithographic pattern on Generation 8.5 glass plates.
 15. The method ofclaim 14, wherein the large-size photomask has dimensions ofapproximately 1220 mm×1400 mm.
 16. The method of claim 14, wherein thepellicle membrane has the following dimensions: outer dimension ofapproximately 1146.0 mm×1366.0 mm and inner dimension of approximately1122.0 mm×1342.0 mm.
 17. The method of claim 1, wherein the large-sizephotomask is configured to form a lithographic pattern on Generation10.5 glass plates.
 18. The method of claim 17, wherein the large-sizephotomask has dimensions of approximately 3400 mm×3000 mm.
 19. Themethod of claim 17, wherein the pellicle membrane has the followingdimensions: outer dimension of approximately 1526.0 mm×1748.0 mm andinner dimension of approximately 1493.0 mm×1711.0 mm.